Many devices for controlling electrical apparatus have a moveable member which the operator turns or slides in order to vary a control signal. Typically graphics are present in the vicinity of the moveable member to indicate the function of the control and to identify settings of the control along the path of travel of the member. Traditionally such graphics are permanently imprinted on a control panel or other structural component of the control device.
It has been recognized that it can be advantageous to replace the permanently imprinted graphics with changeable images produced by an electronic display screen particularly in the case of a control device which is used to control different functions of the controlled apparatus during different modes of operation of the apparatus. The display can change the graphics as needed so that they remain appropriate during each of the different control functions.
The function of the electronic display screen has heretofore been limited to that of visually presenting information to the operator, such as calibration marks, current settings, identifying labels and the like. It has not previously been recognized that an electronic display screen may serve other purposes in addition to displaying information to the operator of a circuit control device.